In recording or reproducing operation of an optical information recording/reproducing apparatus, a high frequency imposing method in which a laser diode is driven by current imposed with high frequency current has been known for preventing laser noise which is induced by return light. The optical information recording/reproducing apparatus using high frequency imposing method, has a high frequency imposing circuit having an oscillator for switching ON/OFF a laser output light with frequency of several hundred MHz, so that vertical mode of laser beam is transformed to multi-mode, and generation of said laser noise is prevented (for instance, JP patent publication 9086/1984).
However, if oscillation frequency component of said high frequency imposing circuit is leaked into air, it is undesirable radiation (line noise, radiation noise). Therefore, the leakage should be prevented.
The radiation of undesired wave is classified to that through air space, and through coupling lines with external circuits. The former is prevented by enclosing an apparatus by conductive shield case, and the latter is prevented by a capacitor coupled between an external coupling line and ground.
FIG. 10 shows a prior optical recording/reproducing apparatus which prevents undesired radiation. In the optical recording/reproducing apparatus in FIG. 10, a portion mounting high frequency imposing circuit is sealed with a shield case 4 (conductive case).
Further, in the optical recording/reproducing apparatus, a laser diode 6 is engaged with an opening on an optical base 7, and the terminals of the laser diode are on substrate 5 for a high frequency imposing circuit, as shown in FIG. 11, which is a view in C-direction in FIG. 10 with a shield case taken off.
The external connection lines for power supply of the high frequency imposing circuit, power supply for a laser diode, and control signal of the high frequency imposing circuit are coupled with an external circuit through a respective through-hole capacitor 11 which engages with a shield case 4. Thus, the high frequency imposing circuit itself is sealed with a shield case, and the external connection lines are coupled with an external circuit through a through-hole capacitor 11, therefore, undesired radiation is prevented.
No radiation leaks through a gap between a through hole capacitor 11 and a shield case 4, by fixing the through hole capacitor to a hole provided on the shield case 4.
The through hole capacitors are coupled with a substrate 5 of a high frequency imposing circuit either through a flexible printed circuit 12 (FIG. 11(a)), or directly (FIG. 11(b)).
However, the prior optical recording/reproducing apparatus which has facility to prevent undesired radiation has the following problems which should be solved.
(1) As shown in FIG. 11, one terminal (a) of a through hole capacitor 11 must be connected to a substrate 5 of a high frequency imposing circuit either through a flexible printed circuit 12 for inner connection, or directly, and the other terminal (b) of the through hole capacitor 11 must be connected to the other flexible printed circuit 13 for external connection, therefore, the operation for mounting a through hole capacitor is complicated, and further it is difficult to reduce cost for components. Further, as a through hole capacitor occupies large area, therefore, it is difficult to reduce size of an optical recording/reproducing apparatus itself.
(2) As a shield case must have a hole for fixing a through hole capacitor, the producing steps of a shield case are complicated, and the assembling steps of the shield case are also complicated.
(3) It is preferable that external connection lines are taken out on one surface of a shield case, when we consider the wiring operation (easy wiring operation, efficiency of wiring operation et al). Therefore, holes for through hole capacitors for power supply of a high frequency imposing circuit, power supply for a laser diode, and control signal of the high frequency imposing circuit must locate on one surface of the shield case. However, this prevents to make small an optical recording/reproducing apparatus.
For instance, if a through hole capacitor is 2 mm.phi., (diameter of a through hole capacitor is 2 mm), the width Wc which a hole occupies is 2 mm as shown in FIG. 10. Assuming that the spacing Ws between the adjacent holes is 1 mm, and the width Wg for ground terminal is 2 mm, then, the total longitudinal length of a side surface of a shield case is around 11 mm. Further, the lateral length must be around 4 mm, assuming that 1 mm of margin is kept on both sides of a hole. Therefore, the area of a side surface of a shield case is 44 mm.sup.2 (11 mm.times.4 mm).
However, as the latest optical recording/reproducing apparatus is small in size, it is almost impossible that a side wall of a high frequency imposing circuit has such a large area.
(4) A laser diode has usually another terminal line for back monitor reception for detecting optical laser output in the same package. When that line is connected to an external circuit, additional through hole capacitor must be installed, and it becomes further difficult to make small an optical recording/reproducing apparatus.
Although it is one of the options to reduce a number of components to make small an optical recording/reproducing apparatus, it is almost impossible to reduce a number of components while preventing deterioration of circuit characteristics. For instance, in a circuit for a high frequency imposing circuit shown in FIG. 12, it is impossible to reduce a number of components (components except for preventing undesired radiation) without deteriorating characteristics. In FIG. 12, D11 is a laser diode, C21, C22, and C23 are a through hole capacitor for preventing noise.
An object of the present invention is to provide an optical recording/reproducing apparatus in which it is easy to mount and assemble components for preventing undesired radiation in an optical recording/reproducing apparatus which has a high frequency imposing circuit, and the mounting space and the cost for those components are decreased.